1. Field of the Invention
The invention relates to tandem systems for circuit-based traffic, and in particular, to tandem systems that use Asynchronous Transfer Mode (ATM) systems to interconnect various circuit-based networks or network elements.
2. Description of the Prior Art
The tandem function is used to concentrate and switch telecommunications traffic in between networks, switches, and other network elements. FIG. 1 depicts the conventional tandem switch known in the prior art. The three switches and the network element are all connected to the tandem switch. The tandem switch allows the switches to connect to the network element without a direct connection between the switches and the network element. It also allows each switch to connect to every other switch without direct connections between all of the switches. This savings in connections and trunking is one of the benefits of tandem switches. Additionally, the connection between the tandem switch and the network element uses bandwidth more efficiently because traffic has been concentrated at the tandem switch. In addition, a tandem switch can be used to concentrate traffic that is going to other networks.
The connections shown on FIG. 1 as solid lines are circuit-based connections. Circuit-based connections are well known in the art with some examples being Time Division Multiplex (TDM) connections, such as DS3, DS1, DS0, E3, E1, or E0 connections. DS3 connections carry a continuous transport signal at 44.736 megabits per second. DS1 connections carry a continuous transport signal at 1.544 megabits per second. DS0 connections carry a continuous transport signal at 64 kilobits per second. As is known, DS3 connections can be comprised of multiple DS1 connections, which in turn, can be comprised of multiple DS0 connections. The signaling links shown as dashed lines may be conventional signaling links with examples being SS7, C7, or ISDN links. The switches shown on FIG. 1 are well known circuit switches with examples being the Nortel DMS-250 or the Lucent 5ESS. The tandem switch is typically comprised of a circuit switch that interconnects DS3, DS1, and DS0 connections.
Those skilled in the art are aware of the costs and efficiencies associated with tandem switches. Many networks cannot justify implementing a tandem switch until the efficiencies gained through the tandem function outweigh the cost of the tandem switch. This is problematic because inefficiencies must be tolerated until they outweigh the high cost of the tandem switch. At present, there is a need for a more affordable and efficient tandem switching system.